The present invention relates to a color image forming apparatus for forming a composite image by superposing image information using electrophotographic technology or the like.
Conventionally, in an image forming apparatus using electrophotographic technology, an image is formed in the manner that an electrophotographic photosensitive body, serving as an image carrier, is charged with an electrifier, this photosensitive body is irradiated with light in accordance with image information to form a latent image, this latent image is developed with a developing device to be visible, and a toner image thus obtained is transferred onto a sheet material or the like.
On the other hand, with the coloring of image, many tandem type image forming apparatus have been proposed until now, in which a plurality of image carriers to each of which such a series of image forming processes is performed are provided, and a full color image is formed in the manner that a cyan image, a magenta image, a yellow image, and preferably a black image are formed on the respective image carriers, and those images are superposed and transferred onto a sheet material at the transfer positions of the respective image carriers. Such a tandem type color image forming apparatus is advantageous for high speed image formation because it has an image forming section for each color.
Such a tandem type color image forming apparatus, as described in, for instance, Japanese Patent Application Ser. No. 11-92598 (Laid-Open Publication No. 2000-284592) of the same assignee, comprises image forming units for forming toner images of the respective colors, i.e., yellow (Y), magenta (M), cyan (C), and black (K), an exposure unit for outputting an image signal to form an electrostatic latent image, an intermediate transfer belt formed into a closed loop and running, and a fixing unit, wherein toner images on the intermediate transfer belt are transferred onto a paper P fed from a paper cassette, and the toner images are fixed to the paper with the fixing unit.
The image forming units for yellow (Y), magenta (M), cyan (C), and black (K) have the same structure, and each unit is the combination of a photosensitive unit including a photosensitive drum on the circumferential surface of which an electrostatic latent image is formed with a laser beam from the exposure unit, an electrifying brush for charging the photosensitive drum with electricity, and a cleaning blade, and a developing unit including a toner supplying tank, a toner supplying roller, and a developing roller brought into contact with the photosensitive drum.
In the conventional tandem type color image forming apparatus, all the image forming units for yellow (Y) color, magenta (M) color, cyan (C) color, and black (K) color are incorporated together in one housing. Therefore, when inspection or maintenance of each image forming unit, the housing is drawn out from the chassis of the image forming apparatus and all the four image forming units are taken out.
On the other hand, a color image forming apparatus is used not only for color image formation using the toners of all colors but also for monochrome image formation using only black color. The frequency of this monochrome image formation using only black is relatively high. Therefore, the frequency of toner supply or inspection/maintenance of the image forming unit for black (K) color is apt to be higher as compared with any other image forming unit.
In the conventional tandem type color image forming apparatus, however, all the four image forming units are incorporated in one housing. Therefore, even when inspection or maintenance of the image forming unit of black (K) color only is to be performed, it is taken out and put in the chassis together with the other three image forming units. Consequently, the image forming units having no need of inspection or maintenance also must be treated, and the user""s handling efficiency is not always good. Besides, since the other image forming units must be taken out and put in every time when frequent inspection or maintenance of the image forming unit of black (K) color is performed, the work load becomes heavy.
It is an object of the present invention to provide color image forming apparatus in which only an image forming unit with high frequency of inspection, maintenance, or the like, can separately be treated, thereby reducing the work load upon inspection/maintenance and making the handling easy.
According to the invention, a color image forming apparatus comprises a chassis for attachment in an apparatus main body, a plurality of image forming units including at least a plurality of photosensitive drums disposed at intervals, and a plurality of developing rollers for developing with toners electrostatic latent images formed on the respective photosensitive drums, and a plurality of housings each provided with open upper ends for respectively accommodating the image forming units while dividing them into a plurality of groups, the housings being independently attachable to and detachable from the chassis, respectively.
According to the structure of the above-described color image forming apparatus, an image forming unit requiring inspection or maintenance is detached from the apparatus by taking out the corresponding housing from the chassis, and a necessary work can be done.
The image forming units are, e.g., four for yellow, magenta, cyan, and black. In this case, it is preferable that the image forming units for yellow, magenta, and cyan are accommodated in first one of the housings, and the image forming unit for black is accommodated in the second housing. With this configuration, since only the image forming unit of black that may be highly frequently used can be taken out from the apparatus, the handling efficiency is improved.
Adjacent ones of the plurality of housings are preferably provided on their opposite surfaces with concavo-convex engagement portions for guiding those housings in the directions of chassis attachment and detachment and for performing vertical positioning. Each housing can easily be performed detachment from and attachment to the chassis and vertical positioning through engagement between the engagement portion of the housing and that an adjacent housing in the chassis.
Each image forming unit may have a casing formed to be inserted in the corresponding housing from above, which has a portion in a shape covering the periphery of the electrifying brush of an adjacent image forming unit. With the provision of such a casing, toner adhering to the electrifying brush of the adjacent image forming unit can be prevented from scattering.